1. Field of the Invention
This invention relates to a gear grinding machine arranged to perform grinding using a threaded grinding wheel, and equipped with a rotary dressing device. The gear grinding machine can modify the wheel pressure angle of the threaded grinding wheel with high accuracy by use of numerical control.
2. Description of the Related Art
A gear grinding machine, in which a gear-shaped workpiece after heat treatment is ground by “a threaded grinding wheel,” a gear grinding tool, to finish a gear, has so far been known. The threaded grinding wheel is an annular grinding wheel having threads (rack teeth) formed spirally on its outer peripheral surface. Grinding is performed, with the positions in an orthogonal coordinate system (positions on the X-axis, Y-axis and Z-axis) of the threaded grinding wheel, and the rotational speed of the threaded grinding wheel being numerically controlled.
As grinding proceeds, the threaded grinding wheel wears, and its sharpness decreases. Thus, after the threaded grinding wheel has ground many gears continuously, the worn-out threaded grinding wheel needs to be dressed by a dressing device to regenerate a sharp cutting edge.
Some gear grinding machines are equipped with dressing devices. Among the dressing devices is a rotary dressing device provided with a rotationally driven disk-shaped dressing tool. With this rotary dressing device, the disk-shaped dressing tool is kept rotationally driven, and brought into contact with the flank of the thread of the threaded grinding wheel being rotated, thereby carrying out dressing.
To modify the tooth profile pressure angle of the gear to be ground, the wheel pressure angle of the threaded grinding wheel has to be modified. Modification of the wheel pressure angle of the threaded grinding wheel is made by dressing the threaded grinding wheel by the dressing device.
To modify the wheel pressure angle, it suffices to turn (turn about a vertical axis (Z-axis)) the disk-shaped dressing tool in contact with the thread of the threaded grinding wheel, although details will be described later.
Among gear grinding machines, therefore, are those of the type having a mechanism for turning the rotary dressing device. With the gear grinding machine having such a turning mechanism, an operator manually turns the rotary dressing device (dressing tool) about the Z-axis by use of a block gauge, which is a tool for turning, to modify the wheel pressure angle.
The necessity for the operator's manual work for turning the rotary dressing device (dressing tool) in order to modify the wheel pressure angle, however, may result in poor accuracy.
Moreover, a gear grinding machine of the type, which cannot turn the rotary dressing device, has hitherto been unable to modify the wheel pressure angle.
The present invention has been accomplished in light of the above-described problems with the earlier technologies. An object of the present invention is to provide a gear grinding machine which can modify the wheel pressure angle of a threaded grinding wheel by moving the position of the threaded grinding wheel to a predetermined position while fixing the position of a dressing tool of a rotary dressing device.